1. Field of the Invention
The present invention relates generally to electrical circuits, and more particularly but not exclusively to phase interpolators.
2. Description of the Background Art
Phase interpolators are widely used to generate a plurality of multi-phase clocks from two clock sources. An ideal multi-phase phase interpolator 100 is shown FIG. 1. The phase interpolator 100 receives two input clocks c1 and c2 and generates (m+1) output clocks, which in FIG. 1 comprise output clocks p0 to pm.
FIG. 2 shows the waveforms for input clocks c1 and c2 and output clocks p0 to pm of the ideal phase interpolator 100. As shown in FIG. 2, the time spacing between the input clocks c1 and c2 is equal to A. In other words, input clock c2 has the same waveform as the input clock c1 except delayed by an amount Δ. The output clock p0 and pm are simply from delaying inverted clocks c1 and c2, respectively, by a specific amount δ. That is, the output clock p0 is the input clock c1 inverted and delayed by an amount δ, and the output clock pm is the input clock c2 inverted and delayed by an amount δ. The other output clocks, i.e., output clocks p1 to Pm-1, are generated by interpolating clocks c1 and c2, and are equally spaced between p0 and pm. With (m+1) output clocks, the time spacing between any two neighboring output clocks is equal to Δ/m, which represents 1 least significant bit (LSB).